The invention relates to a skimmer device for discharging liquid from a centrifuge drum, comprising a vertically arranged skimmer disc pipe and a skimmer disc, which is arranged inside the centrifuge drum and is provided with at least one inlet duct that extends from the periphery of the skimmer disc and empties into at least one shaft duct, which extends at least partially along the skimmer disc pipe, whereby the inlet duct and the shaft duct form a discharge duct, which exhibits at least one throttle point where the cross-sectional area of the discharge duct is reduced.
The volume stream to be discharged from a centrifuge drum through the skimmer device is influenced significantly by the size of the cross-sectional area of the discharge ducts. To increase the cross-sectional areas, several inlet ducts may be provided at the skimmer disc, where said inlet ducts are offset from one another by a certain angle. However, due to the limited area of the skimmer device, the number of radially arranged inlet ducts that are separated from one another by bars cannot be increased arbitrarily.
Alternatively, or in addition, increasing the duct height of each individual inlet duct can be provided in order to increase the maximum volume stream that can be achieved with the skimmer device. However, since centrifuges are often operated with alternating and very different inlet and discharge loads, pressure and volume fluctuations occur, which excite vibrations of the heads of liquid in the ducts, in particular, when the centrifuge is operated at small loads. The vibrations lead to undesirable noise levels and may lead to cavitations in the ducts. In addition, the liquid vibrations may be transferred to the centrifuge drum and in this manner to the centrifuge as a whole.
A centrifuge of this kind is known from DE-OS 37 31 229. Here, several inlet ducts are arranged radially offset to one another in order to increase the discharge load of the skimmer device. A throttle point is located in the shaft duct of the skimmer disk pipe behind the mouths of the inlet ducts of the skimmer device, when viewed in the flow direction. The throttle point results in a strong dampening of the inlet ducts and in this manner prevents the disadvantageous vibrations of the heads of liquid. However, the maximum discharge volume stream that can be achieved with the skimmer device is reduced through the necessary strong throttling.
From the patent DE 696 796, it is known to provide two ring-shaped shaft ducts that are arranged concentric to one another and that are guided in the skimmer disk to its periphery in ducts that are arranged on top of each other. One of the ducts is used as a discharge duct for the liquid drawn from the centrifuge drum and the other for supplying carbonic acid to the centrifuge drum. A utilization of this additional duct, which is provided for the gas supply, for withdrawing liquid is not disclosed. In addition, vibration problems occur with these two ducts as well. Furthermore, the design of concentrically arranged ducts that are nested in one another is elaborate in both design and manufacture.